You say it is proven, but actually the study linked to by the article you mentioned from The Atlantic does not claim that. In the summary, it says: "The evidence does not suggest necessarily a relationship between tax policy with regard to the top tax rates and the size of the economic pie, but there may be a relationship to how the economic pie is sliced." And indeed the study's data does not prove any of this, so it is correct in not making that claim.
> If you do, on what sensible grounds can you criticize the government for paying up? The government is obeying the rules of this capitalist system.
The government also decided that the system would be this particular not very capitalist system, where it pays contractors for anything at all. That is what it ought to be criticized for.
> Even if it always was required to choose the cheapest bid, one could still allege that is waste. At which point, your ideology is blaming the government for “wasting” resources when there are no other options, and—with no evidence provided—concludes the answer is to starve the government of resources to use for the public good.
There is at least one other option: not having the government choose any bid at all, cheapest or not. And there is an even better option: not having a government in the first place.
> Is there proof that raising taxes causes economic growth? No. That claim is not made.
It has been made by dnomad: "There is very convincing evidence that higher taxes and greater government spending do lead to long term economic growth."
> What is shown is that cutting taxes does not spur economic growth, as those who advocate for that idea claim.
The study does not claim that it shows this, and if it did it would be wrong as it presents no evidence that this is the case.